What Does Control Mean in Scientific Terms?

James Lind was the first to carry out a controlled experiment to develop a cure for scurvy in the year 1747. He performed his experiment on sailors who had developed scurvy.

Scientific method is defined as a set of procedures that need to be followed in order to attain new scientific knowledge in a systematic manner. Although scientific methods can be altered, the process follows a few logical steps.

• First, there has to be a question for which one needs to find an answer; for example, why does a particular phenomenon occur?
• The second step is to make a proposition based on the knowledge available as to why the phenomenon occurs. This is called stating a hypothesis.

• The third step is to deduce logical consequences that may occur due to the hypothesis.
• The next step involves designing and performing of different experiments to test these deductions.
• The final step of a scientific method is to analyze the result obtained to determine if the hypothesis is right.

For an experiment to be successful, the results obtained should be comparable to others, accurate, and reproducible. A scientific control or control in an experiment determines its reliability and accuracy. A control can be defined as a reference or a standard result to which the results of the factor being tested is compared.

In simple words, to determine how tall a person is, we must compare the height of the person to other people; only then can we comment on the tallness or the person being tall or short. A control minimizes the effect of other factors that may alter the results of an experiment.

Ideally, for an experiment to be reproducible and accurate, all other factors that may affect the outcome of the experiment need to be specified. These factors are sometimes called controlled variables. This ensures that the results that we obtain are solely due to the factor being tested.

For every experiment that is performed, there has to be a set of controls for it. These controls not only determine the accuracy of the experiment, but also help interpret the results obtained.

They can be classified as:

✦ Positive control
✦ Negative control

In positive control, the experiment is performed in such a way that a positive result is the desired outcome of the procedure. Visually, a positive control is identical to the positive result that may be generated by the factor being tested.

Let us consider an example―while performing an assay to determine the presence of protein in a test solution. We might take a protein solution of a known concentration as the positive control. We know that the result generated will be positive. We can generate a Standard Dose Response curve to determine the concentration of the protein in the test solution.

In a negative control, the experiment is performed in a way such that a negative result is the desired outcome of the procedure. This is visually identical to the negative result that may be generated by the factor being tested.

Continuing with the given example, we might take distilled water in place of the protein solution as the negative control. Here, we expect the result that will be generated to be negative.

The results of the positive and negative controls can be compared to the result that will be obtained from the test solution. This will help us comment on whether the protein is present or not.

If for some reason, the results of the controls are different than what we expected, we can say that there must have been an error while performing the experiment, or there might be something wrong with the chemicals that were used.

In order to determine the efficacy of a drug, the control group is usually given a placebo drug, and the test group is given the drug that is being tested. The members of the two groups are usually chosen at random to ensure that the population is diverse.

The results of the two groups are compared, only if there is a significant improvement in the individuals belonging to the test group as compared to the individuals belonging to the control group; the drug is said to be effective.

✦ For testing the antimicrobial activity of the test, we provide a negative and positive control. The negative control will be buffer or distilled water (which is used to dissolve the antibiotic and the test to perform the experiment) only, and the positive control will be an antibiotic dissolved in an appropriate buffer or distilled water.

Here, the results of the positive control and the negative control are compared to the results of the test to determine its antimicrobial activity.

✦ For testing, if a test fertilizer promotes shoot growth, we may provide plants belonging to the negative control group with only water for its growth. The plants belonging to the positive control group are given water and fertilizer, which is known to promote shoot growth, and the plants of the test group are given water and the test fertilizer.

Again, the results of the positive and negative control are compared to the results of the test fertilizer by comparing the lengths of the shoots of the plants. 

For performing controlled experiments, all the parameters need to be specified including the species and the strain of the organism that we perform the experiment on.